Nafion((R)) membrane is a key component of polymer electrolyte membrane fuel cell. In this paper, transmission and attenuated total reflection (ATR) spectra of Nafion((R)) membrane and the difference of absorption peaks between two modes are presented. The peak shift is attributed to the different chemical environments of surface and bulk. Obvious change was observed after thermal treatment on Nafion((R)) membrane through calculation of the relative absorption intensity ratio of different groups. It was found that side chain may move out of the bulk to the surface for the membrane. And the moving degree increased with the treating temperature. (C) 2004 Elsevier B.V. All rights reserved.